A radar apparatus utilizing a millimeter wave is well known as an apparatus for measuring, when a vehicle is running, the distance to an obstacle or a preceding vehicle. The radar apparatus radiates a radio wave and receives the radio wave reflected from an target such as an obstacle and a vehicle. This radar apparatus detects the intensity of reflected wave received, Doppler shift of frequency, and a propagation time up to reception of the reflected wave from radiation of the radio wave and measures a distance to the target and a relative speed from the result of detection.
Several systems are provided for radar modulation used for the purpose explained above, and the typical methods are FMCW (Frequency Modulated Continuous Wave) system and two-frequency CW (Continuous Wave) system.
Japanese Patent Laid-Open No. H10-253753 discloses a radar system and a radar apparatus for obtaining a distance and a speed of a target as a function of phase difference of a receiving signal corresponding to each ramp by sending alternately at least two kinds of parallel and non-continuous frequency modulation ramps.
Moreover, Japanese Patent Laid-Open No. 2004-151022 discloses an FMCW system and an FMCW apparatus employing a frequency pattern giving two or more frequency slopes to a transmitting wave.